1. Field of the Invention
The present invention relates generally to a support column and more specifically to an improved extendable/retractable column for use in supporting elevated structures that can be extended from a portable or fixed platform or other substrate
2. Description of the Prior Art
Structures that comprise one or more elements that can be linked together to form a rigid column or other structure are well known in the art. Structures of this kind may be used to form an elevated or elevatable platform to elevate a person or equipment or to support other structures relative to a supporting substrate or platform. See U.S. Pat. Nos. 2,661,082; 3,397,546; 4,024,595; 4,089,147; 4,237,662; 4,920,710 and 6,112,474.
Extendable/retractable towers (or simply “retractable towers” as they may be referred to herein) of this kind may be further utilized as portable telecommunications towers where various sites can be tested without constructing a costly, permanent test tower. Retractable towers may also be used as supports for temporary lighting systems for sporting events, emergencies, on ships or the like. In general, retractable columns or towers may be used for any application where it is desired to provide a support for a person or equipment at an elevated location relative to a reference platform or substrate.
Retractable towers or columns of the general type to which the present invention relates are shown and described in U.S. Pat. Nos. 4,920,710 and 6,112,474. In general, these patents disclose a retractable column formed from three link chains or three flexible webs. These chains or webs are linked with one another as they are vertically extended to form a tower with a generally triangular cross-section. In these patents, the three link chains or three flexible webs are each stored on a rotatable take-up mechanism located at or near the level of the platform or other supporting substrate. During operation, each of these three link chains or flexible webs is centrally directed so that the link chains and the flexible webs are connected with one another and driven vertically. Accordingly, each of the retractable columns in these patents also includes means for interconnecting the three link chains or flexible webs together and means for driving those elements vertically upwardly.
In U.S. Pat. No. 4,920,710, the interconnection means includes the provision of hook members extending laterally outwardly from corners of each chain member for interconnection with corresponding outwardly extending hook members of an adjacent chain member. In U.S. Pat. No. 6,112,474, this interconnection means is in the form of a set of teeth located along opposite edges of the webs with each of the teeth having a neck and a crown region larger than the neck.
The drive mechanism in U.S. Pat. No. 4,920,710 includes a plurality of rotatable tooth gears positioned within the triangular column which engage corresponding toothed racks on at least two of the chain members. These toothed gears are rotatable about a horizontal axis. In U.S. Pat. No. 6,112,474, the drive means includes a drive roller associated with each of the flexible webs. Each of these drive rollers is rotatable about a horizontal axis and is located outside the generally triangular column. Each roller engages a series of spaced openings in each of the continuous webs.
Although prior retractable columns have been satisfactory for some applications, significant limitations exist due to the nature of the drive mechanisms, the means for providing stability to the column during and after erection, the means for vertically supporting the columns and the complexity of the structures, among others. Accordingly, there is a need in the art for an improved extendable and retractable tower or column structure that overcomes these limitations.